Abstract: Studies on the characteristics of the Reservoirs, lithology and the controlling factors of 4+5th member of Yanchang Formation in Fanxue area of Dingbian oilfield in Ordos basin show that the lithology of the reservoir of 4+5nd member are mainly arkose and lithic feldspar sandstone, with sorting from medium to good, and a poor psephicity. The pore types are mainly residual intergranular pores and dissolution pores, accounting for 59%, 34% of the total pore respectively. The porosity of the reservoir ranges from 0.2% to 17.6%,with the average of 8.5%. The permeability ranges from 0.1×10^-3 to 0.4×10^-3 μm²,with the average being 0.25×10^-3 μm². The main cements are carbonate, clay and quartz. The contents of sedimentary component, carbonate and clay cement have important impact on the reservoir quality. The reservoir with higher content of rigid particles, lower content of plastic particles and carbonate cement has good quality. The reservoir with higher content of plastic particles has lower porosity and permeability because of compaction, while the reservoir with higher content of carbonate cement has lower porosity and permeability because of carbonate cementation. The porosity and permeability of reservoir increase with the higher content of rigid particles and the lower content of plastic particles and carbonate cements.